The present invention relates to a control system for a servomechanism device such as robot. More particularly, it relates to a position correcting control system for a servomechanism device which is well suited to perform high-precision positioning or high-performance operations on the basis of a sensor feedback control system such as force detection feedback control.
FIG. 3 shows an industrial robot which is an example of a servomechanism device. This robot 1 has, e.g., six degrees of freedom and exerts an action on an object to-be-handled (not shown) by means of a hand 2. A controller 3 receives the reference values of positions and forces and feeds back position signals and force signals, thereby to deliver manipulated variables. The manipulated variables are applied to the motors of corresponding joints, and the position of the acting point of the hand 2 is controlled so as to coincide with the reference value thereof. In general, such a device is directly controlled by the rotational positions of motor shafts, and distances from the motor shafts to the acting point of fingers are found through correcting calculations based on the specifications of the mechanism. Since, however, the specifications of the mechanism fluctuate greatly, the control precisions of the position and attitude of the fingers are not very high. Therefore, the position and attitude of the fingers are detected only within a limited range by another sensor, for example, a six-axis force sensor 4, thereby to intend a precise feedback control.
Statements on the sensor feedback control of this type are contained in `Journal of the Japan Society of Precision Engineering`, Vol. 51, No. 11, pp. 40-45 and pp. 46-52; `Journal of the Society of Instrument and Control Engineering`, Vol. 25, No. 1, pp. 77-80 and pp. 45-50; and `Preliminary Abstracts of the 27th Japan Joint Automatic Control Conference`, pp. 241-244. In these literatures, however, a method of constructing a control system and practicable methods of correcting a position and an attitude, as well as the quantitative evaluation of the effects thereof are not described in detail, Such descriptions lack information for, accurate designing of various items of the whole system. Moreover, as regards the control employing the force sensor, control purposes differ significantly. It would be desirable that a position error is detected on the basis of a force which is used it for the feedback control; a pressing control under a predetermined force may be utilized and a force may be detected which causes bending of the fingers backwards by a distance corresponding to the magnitude of the force.